THE IMPACT OF VARIOUS DOSES OF “EXPERT NPK 20–20–20+TE“
APPLICATION ON THE YIELD AND SOME OTHER
OF LETTUCE (LactuvaSativaL.)
Lettuce (Lactucasativa L.) which is an annual plant of the daisy family, Asteraceae is a
broad green leafy vegetable. As a cool climate plant, it is most often grown during winter in
warm climates, whereas in summer in cold climates (Günay 1992). Botanists and researchers
have different opinions about the homeland of lettuce and its spread around the world. Lettuce
was first cultivated in Egypt in 4500 BC (Ryder 1979), its wild forms were reported to have
spread throughout Central and Southern Europe, the Canary Islands, Algeria and Abyssinia,
and north Indian regions such as West Asia, the Caucasus, Kashmir and Nepal. Consequently;
it has been accepted that its homeland is a large area that includes Europe, Asia, and North
Africa (Vural et al. 2000).
The growing time of lettuce, which is available at grocery stores all year round, is 60–
90 days. It can be grown twelve months of the year with varieties that have been bred in
accordance with different seasons both in the open and under cover. It is among the most
produced and consumed vegetables in Turkey. When the production and eating habits are taken
into account, it has been observed that butterhead lettuce and curly lettuce types are the most
preferred ones. It is extremely easy to grow lettuce; however, timely care is critical when high
yield and quality are targeted from lettuce cultivation.
Lettuce cultivation is carried out in the temperate regions of our country in autumn, winter or
early spring. (Eşiyok et al. 1996).
Lettuces are grouped into four botanical variants according to leaf characters:
Lactucasativa var. capiata: Head lettuce,
Lactucasativa var. crispa: crisphead lettuce,
Lactucasativa var. longifolia: Romaine lettuce,
Lactucasativa var. Angustana: Asparagus lettuce.
Top lettuce producers, China and the USA, contribute 65% of the world’s production.
Our country also plays an important role in the production of world lettuce. As of 2015, an area
of approximately 218,353 decares (including under–cover cultivation) was cultivated, and
lettuce production has soared up to 516,439 tonnes over the last decade (Anonymous, 2015).
Lettuce is a rich source of vitamins and minerals, and at the same time an appetizing
and nutritious fresh vegetable (Günay 1981). Lettuce leaf which is an indispensable vegetable
of diets, is made up of 94–95% water and contains 6–8 mg of ascorbic acid, 1–1.5 g of raw
protein, 0.2–0.4 g of fat, 1.5–2.5 g carbohydrates, 330 IU Vitamin A, 20–25 mg of calcium, 40
mg of phosphorus, and 1.5 mg of iron (Vural et al. 2000).
The optimum temperature for germination is around +15 °C and the optimum
temperature for growth is +15 – 18°C. Lettuce seedlings with 6–10 leaves are resistant to cold
temperatures up to 0 – 5 °C (Ozturk 2011). The favorable temperature for tying lettuce head up
is between +8 – 12 ºC. The transition from vegetative to generative phase starts at temperatures
higher than +18 ºC. Non–flowering summer varieties which are resistant to high temperatures
have been developed through the breeding studies carried out in recent years.
Lettuces are superficially rooted plants with a main root that stretches 15–20 cm and side
roots that spread around it with a width of 20–30 cm. Although it is not very selective in terms
of soil requirements, in order to get quality products, it should be grown in soils rich in organic
matter, humus and nutrients (especially up to 25–30 cm in depth), and in well drained deep and
loamy soil with high moisture retention capacity. Loose–leaf lettuce grows well in soils with
pH 6–7; whereas, head lettuce with pH 5.5–7. Plant development in heavy soils abates and the
head weight decreases.
Although the yield values for loose–leaf and head lettuce cultivation vary depending on
many factors such as variety, climatic conditions, growing period, number of plants in the unit
area, the yield value between 3–4 kg/m2 is reported to be good (Aybak 2002). Efficiency and
quality improvement can be achieved by conscious and balanced fertilization in addition to
other production dynamics.
Saraçoglu (1997) conducted a study to determine how different dosage use of nitrogen
and potassium affects the development, yield, and quality of the hydroponic cucumber in
greenhouses. 100, 200, and 300 ppm doses of nitrogen and 9 different nutrient solutions of
potassium were used fort his trial. It was found out that the nitrogen is effective on plant
development, yield, and quality. However; 300 ppm nitrogen application causes a decrease in
shoot thickness, root length, and the root wet weight. It has been observed that both early and
total yield decreased when 300 ppm of nitrogen applied. On the other hand, different doses of
potassium applications have no effect on plant development characteristics and yield but only
on body thickness. Potassium was found to be effective on average fruit weight. However, the
fruit weight decreased when 100 ppm of potassium nutrient solution applied. It was observed
that the nitrogen doses applied did not lead to any difference in terms of fruit weight; but the
fruit weight decreased linearly as the nitrogen dose increased. Total water soluble dry matter
and titratable acidity increased in parallel with the increase of nitrogen dose; but no change has
been reported after potassium applications. The pH of the fruit juice increased as nitrogen dose
increased; whereas, when potassium dose increased, the pH of the fruit juice decreased linearly.
When the correlation between the severity of the symptoms of the powdery mildew disease and
the doses of nitrogen and potassium applied was examined, the simple and interactional effects
of nitrogen and potassium were both found to be significant. Applications of 200 ppm nitrogen
+ 200–300 ppm potassium have reduced the symptoms of powdery mildew. The researcher
stated that the nutrient solution to be used in the cultivation of cucumbers in perlite should not
exceed the nitrogen content of 200 ppm and the potassium content should be in between of 200–
Dark, (1999) examined the effect of graded doses of potassium on the development and
quality characteristics of greenhouse carnations. In his two–year trial, he applied 4 different
doses (0, 10, 20, 30 kg/da) of potassium sulfate before planting. As basic fertilization, he applied
30 kg/da ammonium sulfate and 10 kg/da triple super phosphate. While the impact of increased
doses of potassium on the quality criteria of the carnation plant was found to be statistically
significant, the most positive results were obtained from 10 kg/da and 20 kg/da potassium
2. RESEARCH MATERIAL & METHOD
2.1.1. Vegetative Material Used in Research
This study was carried out on Maritima lettuce in 50x18x16 cm size balcony type pots.
For this research, the pea–perlite mixture was used in a ratio of 3:1 and placed into
balcony–type pots. Three seedlings were planted per pot and only doses of 0, 5, 10, and 15 kg/da
were taken into consideration for this trial. Fertilizer was given in equal quantities twice on the
15th and 25th days after planting. Randomized blocks were established with 3 repetitions.
During this study, all cultural processes were carried out, allowing the plants to reach the
marketable harvest size. The harvesting process took place on the 68th day by cutting the plants
with the help of a sharp knife without damaging the shoot just above the soil level.
In this study; the yield (g/plant), leaf width (cm), leaf length (cm), number of leaves
(piece/plant), leaf SPAD value, % dry weight values (g/100 g), vitamin C content of the leaves
(mg/100 ml of sap), leaf color (Minolta CR–400 color meter, KonicaMinolta, Japan) were
measured. Statistical data analyses were carried out in JUMP package program. The trial pattern
constituted of randomized blocks with 3 repetitions. Each pot was considered as a repetition.
The significant difference between the averages of interaction between nitrogen doses,
potassium doses and nitrogen doses*potassium doses was calculated by LSD multiple
comparison test. Significant differences between averages were reported at p<0.05 importance
All harvested plants were weighed by a scale with a precision of 0.01 and the yield is
calculated as g/plant.
2.3.2. Leaf width
Randomly chosen 6 leaves among the outer 2nd and 3rd leaves of the plant were
measured from their widest sides with the help of a ruler.
2.3.3. Leaf Length
Randomly chosen 6 leaves among the outer 2nd and 3rd leaves of the plant were
measured from their longest sides with the help of a ruler.
2.3.4. Number of Leaves
It was calculated by counting the leaves of the harvested plants.
2.3.5. Dry Matter Ratio
After the samples were placed in the paper bags, they were weighed and their net
weights were scaled. The same samples were dried for 72 hours at 65 ºC, and then the dry
weight ratios were compared with the fresh weight values.
2.3.6. Vitamin C Content of Leaves
10 g of leaf sample and 100 ml of 0.4% oxalic acid solution were mixed and blended
for 5–6 minutes. After straining the blended sample with a filter paper for a while, they were
put into a centrifuge with a speed of 6000 minutes/sec for 6 minutes. When the residue settled
down in the centrifuge, 1 ml of the strained limpid part of it was taken and diluted by 10%.
Afterwards, through 2,6–dichloroindophenol indicator dye vitamin C mg/100 ml sap was
determined by using a 518 nm wavelength spectrophotometer (Pearson, 1970).
3. FINDINGS & DISCUSSION
3.1. Yield (g/plant)
The effect of different doses of Expert NPK 20–20–20+TE on lettuce yield was found to
be statistically significant (P<0.05). In Expert NPK 20–20–20+TE applications, the highest yield
(374.67 g/plant) was obtained from 15 kg/da application; whereas, the lowest yield (214.83
g/plant) was obtained from the control blocks. Obviously, Expert NPK 20–20–20+TE
applications enhanced the efficiency up to 15 kg/da. Thus, fertilizer application has a positive
effect on the lettuce yield. In 15 kg/da Expert NPK 20–20–20+TE application, where the highest
efficiency was obtained, a 54% yield improvement was achieved when compared with the
3.2. Leaf Width (cm)
The interaction between the different doses of Expert NPK 20–20–20+TE applications
and the leaf width was found to be statistically significant (P<0.05). Different doses of Expert
NPK 20–20–20+TE applications revealed that the minimum leaf width value (11.33 cm) was
obtained from the control block.
3.3. Leaf Length (cm)
The data obtained from the trial revealed that the impact of Expert NPK 20–20–20+TE
applications on the leaf length of lettuce was statistically significant (P<0.05). The shortest leaf
length (11.87 cm) was obtained from the control block; whereas, the longest leaf length (18.88
cm) was obtained from the blocks of 15 kg/da application. Potassium application resulted in
longer leaves. The outcomes of all applications address longer leaves with respect to the control
3.4 Leaf Number
The effect of nitrogen and potassium applications on the leaf number of lettuce plants
was found out to be insignificant (P<0.05). According to the trial results, the leaf number varies
between 23.17 – 24.50 piece/plant.
3.5. Dry Matter Ratio (%)
The interaction between the nitrogen and potassium applications and the dry matter ratio
values in lettuce was found out to be statistically significant (P<0.05). In this trial, the highest
rate of dry matter (6.07% ) was obtained from the blocks of 15 kg/da application and the lowest
dry matter ratio was obtained from the control blocks.
3.6. Vitamin C Content of Leaves (mg/100 ml extract)
The interaction between the nitrogen and potassium applications and the values of
vitamin C in lettuce leaves was found out to be statistically significant (P<0.05). The highest
amount of vitamin C was obtained from the blocks of 15kg/da application; whereas, the lowest
amount of vitamin C was obtained from the control blocks. As the dose of application increased,
the amount of vitamin C in lettuce leaves increased as well.
4. CONCLUSION & RECOMMENDATIONS
High–end high yield in lettuce cultivation can be achieved with a balanced fertilization
and its use on appropriate varieties in a timely caring manner. This study revealed that the
number of fertilizer applications and the leaf width, which is accepted as one of the quality
parameters for lettuce, are directly proportional. Similar results were observed also for leaf
In this trial, no relation has been detected between the number of lettuce leaves which
varied between 23.17– 24.50 pieces/plants, and the fertilizer applications. Especially, the
presence of large and small leaves on the head of the curly endives variety rendered it difficult
to determine the number of leaves. In addition to this, very likely, due to its genotypic properties
the upper limit in the leaf number has already been reached.
In this study, the highest rate of dry matter was obtained from the blocks of 15 kg/da
application. The trial result indicated an increase in the amount of dry matter which found out
to be directly proportional to fertilizer applications.
In terms of vitamin C values, the highest values were obtained from the blocks of 15
kg/da applications. Substantially; as the nitrogen, phosphorus and potassium rates increased,
the value of vitamin C was also increased. Contrary to the widespread belief, this study revealed
an increase in vitamin C values even when the fertilizer rates increased.